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Surely this is one of the oddest, on-screen pairings in years. Natalie Portman gets nominated for Oscars, Ashton Kutcher gets nominated for Razzies. She’s fluent in Hebrew, he barely gets by with English. She dances ballet, he tweets.

No, not Benjamin Millepied, the dancer and choreographer to whom she is now engaged, and with whom she is now expecting a baby. I’m fine with that.

I’m talking about her co-star in the new Ivan Reitman romantic comedy “No Strings Attached.” She plays Emma, a doctor with a schedule too busy to accommodate a boyfriend. So she begins a strictly physical relationship — no strings attached — with a friend, Adam, who has a reputation for sleeping around.

Surely this is one of the oddest, on-screen pairings in years. She gets nominated for Oscars, he gets nominated for Razzies. She’s fluent in Hebrew, he barely gets by with English. She dances ballet, he tweets.

Most importantly, of her 26 films on the Rotten Tomatoes website, 18 have positive — or "fresh" — ratings. She makes good movies. Of his 16 films listed on the site, none, zero, zilch, have been rated fresh. He makes crap.

My knee-jerk, almost visceral reaction to him isn’t based solely on these films, however. It’s based on all the other media stuff that seeps into our consciousness despite our best efforts to keep it out.

He produced and hosted the MTV reality show “Punk’d,” an update of “Candid Camera.” Except Kutcher went for celebrities rather than plain folks — making the whole thing feel incestuously Hollywood — and he changed the tone. Some of the cruddier aspects of our culture can be heard in the transformation of the show’s catchphrase: from “Smile! You’re on ‘Candid Camera’!” to “You’ve been punk’d!”

Then there are those Nikon camera ads in which Kutcher, at weddings and restaurants, seems inordinately pleased with himself (“Boo-yah!”) for taking ordinary photos. This, in fact, may be the essential Kutcher personality: exuding extreme, almost obtuse self-satisfaction for doing not much.

Still, it seemed only fair to check out some of his movies. I ended up watching two. OK, I made it through some of “Spread” and 15 minutes of “Killers.”

In the latter, Kutcher is cast against type. He played pretty and dumb in “That ‘70s Show,” then hapless and dumb in rom-coms over the last 10 years, but in “Killers” he’s suddenly a bona fide secret agent, supersmart and supercool, who says things like, “I’ve got a visual on him now. Target confirmed.” It’s painful.

He’s also supposed to be so overwhelmed by Katherine Heigl’s klutzy character that he’s willing to give up this life for a house in the suburbs and weekend barbecues. Except he exudes nothing like love or desire or charm. He exudes nothing. He’s flat. He shows up in a swimsuit in a high-class hotel and Heigl is charmed by his body. That’s it. Basically he’s a male starlet. His entire career is proof that female fans can be as shallow as men.

“Spread” actually plays off this girl-toy image by casting him as Nikki, a would-be actor and current gigolo to the older, richer ladies of L.A. He tells us in voice-over, “I don’t want to be arrogant here, but I’m an incredibly attractive man.” He dispenses relationship advice for a-holes: “Never show you’re impressed — it lowers your market value.” Of course there’s comeuppance. But for most of the movie he’s a self-satisfied jerk.

Kutcher has a moment, though. At one point Nikki is relegated to a dive hotel and, desperate, calls his family back home and talks to his mother. But he lies to her and she hangs up on him. Even she can’t abide him. His mother. And he breaks down. It’s a moment that feels deep and personal. He’s wholly convincing here.

Which means Kutcher is as good for 15 seconds as Natalie Portman has been for 15 years.

Set aside quality for a moment. Doesn’t she know her own oeuvre? Her characters are not supposed to fall for characters like Kutcher. They’re supposed to fall for someone like ... well ... us: the ordinary (Timothy Hutton, Zach Braff), isolated (Hugo Weaving, Jean Reno) and nerdish (Lucas Haas, Melchior Beslon, Jason Schwartzman).

No movie star as pretty as Portman has wound up with so few handsome leading men. She dates down in the movies. Then she breaks our hearts by being too young, devilish or smart. She plays enigmas. Is she still with us at the end of the movie? Sometimes it’s hard to tell. Yes, says “Paris, je t’aime.” No, says “Closer.” Maybe, says “Hotel Chevalier.” In “Black Swan,” she even breaks up with herself.

Was “Black Swan” too much for her? For a year she played Nina, a demanding, physical role in this intense, psychological drama, then immediately took on light and carefree parts. “No Strings Attached” is just the first salvo. In April, she plays an ass-kicking medieval warrior in the comedy “Your Highness.” In July, she plays Jane Foster, the blankest of superhero girlfriends, opposite the Son of Odin in “Thor.” All three look awful.

So is this trend a reaction to playing Nina or a continuation of playing Nina? “Black Swan” is all about duality, after all. Nina, a technically perfect ballet dancer, wins the lead in “Swan Lake” but is encouraged to display her wilder, more carefree side. Her director tells her she needs to be less like herself (white swan) and more like the wild child, Lily (black swan), played by Mila Kunis, Kutcher’s former co-star on “That ‘70s Show.” Lily then becomes Nina’s friend, rival, doppelganger, nightmare. Nina sees her everywhere, fears she will take away her coveted role, even as, in the end, Nina is able to tap into her wild side.

Is this what Portman is doing now? Letting loose her black swan? Giving up the technically perfect (“Paris, je t’aime”) for the carefree (“Your Highness”), and leaving critics like myself to channel Nina’s horrible mother and wonder what happened to their "sweet girl"?

Except, for the most part, critics aren't doing this. Early notices of the film have been mixed but leaning positive. In fact, “No Strings Attached” may give Ashton Kutcher his first “fresh” film ever. Natalie Portman may in fact save his career.

Straight arrow

Portman plays a warrior princess in 2011's "Your Highness," starring alongside James Franco and Danny McBride. The film has been called "a medieval stoner comedy."
(Universal Pictures)
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Megawatt smile

Portman arrives at the premiere of "No Strings Attached" in Los Angeles on Tuesday, Jan. 11, 2011. The film received mediocre reviews but did better than expected at the box office.
(Matt Sayles / AP)
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Mismatched couple?

In 2011 comedy "No Strings Attached," Portman plays a doctor who tries to keep her relationship with Ashton Kutcher purely physical. The film topped the box office on its debut weekend, beating Seth Rogen's "The Green Hornet."
(Paramount Pictures)
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He does want to sleep with me

While accepting her best actress Golden Globe for "Black Swan," Portman thanked Millepied, who plays a small role in the film as a dancer with no sexual interest in the neurotic Nina. "It's not true! He totally wants to sleep with me!" she said. Her nervous laugh after delivering the joke was repeated and drawn out into a viral video that quickly made the rounds on the Internet.
(Handout / Getty Images)
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Parents to be

Portman and Millepied arrive at the Golden Globe Awards on Jan. 16, 2011 in Beverly Hills, Calif. He was born in France and raised in Senegal, beginning ballet training at age 8 with his mother, herself a ballet dancer. He reportedly left the ballerina with whom he was living when he and Portman fell in love on "Black Swan."
(Jason Merritt / Getty Images)
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Beauty in black and white

Natalie Portman won the best actress award at the Critics' Choice Awards on Jan. 14, 2011 in Los Angeles. She thanked "Black Swan" director Darren Aronofsky, joking "You made me very skinny and you ... made me fat," referring to the workouts she took on for the role and to her eventual pregnancy with and engagement to choreographer Benjamin Millepied.
(Jason Merritt / Getty Images)
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Dark side

In 2010's "Black Swan," Portman plays nervous and naive ballerina Nina, who can play "Swan Lake's" innocent white swan easily, but struggles to understand the role of the sensual black swan.
(Reuters)
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Bringing hope to the world

Portman speaks at the 25th anniversary of the Foundation for International Community Assistance in November 2010. She is an ambassador of hope for the group, which promotes the use of micro-finance to provide financial services to the world’s lowest-income entrepreneurs. Portman has visited FINCA programs in Ecuador, Guatemala, Mexico and Uganda and often speaks on its behalf.
(Joe Corrigan / Getty Images for FINCA)
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War story

In 2009's "Brothers," Portman plays a mom and wife who's suddenly left a widow, or so she believes. But her husband, played by Tobey Maguire, makes an unexpected return, only to find that his brother (Jake Gyllenhaal) has fallen for Portman's character.
(Lionsgate)
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Giving out the gold

The city that never sleeps

In 2009, Portman starred in "New York, I Love You," a collective work of 11 short films about the city. It's the second in a series called the "Cities of Love" franchise. 2006's "Paris, je t'aime" was the first.
(Vivendi Entertainment)
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Putting her best foot forward

Portman was a vegetarian since childhood and became a vegan in 2009, reportedly after reading Jonathan Safran Foer's book, "Eating Animals." The year before that, she launched a line of vegan footwear, seen here.
(Astrid Stawiarz / Getty Images)
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Losing her head

Portman played the famous Anne Boleyn and Scarlett Johansson her lesser-known sister Mary in 2008's "The Other Boleyn Girl," based on Philippa Gregory's novel.
(Columbia Pictures)
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Bluer than blue

In 2007, Portman starred with Norah Jones in "My Blueberry Nights," the first English feature film directed by Hong Kong filmmaker Wong Kar Wai. Portman plays a poker player who's lost all her money gambling.
(The Weinstein Company)
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Going ape

In 2007, Portman teamed up with wildlife expert Jack Hanna to make "Gorillas on the Brink," a TV special about the plight of gorillas in Rwanda.
(Animal Planet)
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Double role

Portman plays two characters in 2007's "Goya's Ghosts," set in Spain in the 1700s. She portrays both a young model and her lookalike, a prostitute.
(Samuel Goldwyn Films)
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World of 'Wonder'

Portman plays an employee in a magical toy store run by Dustin Hoffman in 2007's "Mr. Magorium's Wonder Emporium." She told the press she was excited to make a movie for children.
(Fox-Walden)
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Rap it up

In 2006, Portman spoofed herself in an SNL Digital Short on "Saturday Night Live." She turns her good-girl image on its ear by playing herself as an angry gangsta rapper, saying when she was at Harvard she did drugs constantly and cheated on every test.

Who needs hair?

Portman wasn't afraid to shave her head for 2006's "V for Vendetta," an adaptation of the comic book series of the same name. Her character joins an underground anti-government group. Jerusalem-born Portman has been quoted as saying "being from Israel was a reason I wanted to do this because terrorism and violence are such a daily part of my conversations since I was little."
(Warner Bros.)
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Close to you

Portman and Clive Owen starred in 2004's "Closer," often mentioned as one of the actress' best films. Both Owen and Portman were nominated for supporting-acting Oscars for their roles. Neither won, but they did win Golden Globes.
(Columbia Pictures)
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Smile for the cameras

'Garden State'

Portman, Peter Sarsgaard, left, and Zach Braff, right, starred in 2004's "Garden State." Portman's character was an epileptic and a pathological liar. Braff wrote and directed the film, which had only a limited release in theaters but gained more attention on DVD.
(Fox Searchlight)
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Giving birth at Wal-Mart

Portman starred in the 2000 film "Where the Heart Is," based on the best-selling Billie Letts novel. She plays Novalee Nation, who is abandoned by her boyfriend at a Wal-Mart and decides to live there, even giving birth to her baby in the store.
(20th Century Fox)
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Luke, I am your mother

Portman gained real fame in 1999 when she played Queen Padme Amidala in the first of the three "Star Wars" prequels, "The Phantom Menace." Her marriage to Anakin Skywalker, who later becomes Darth Vader, produces twins Luke and Leia, but she dies giving birth to them.
(20th Century Fox)
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Working with Woody Allen

Getting her start

Natalie Portman was just 13 when she made her feature film debut, as a child who befriends a middle-aged hitman (Jean Reno) in 1994's "Leon: The Professional." Born Natalie Hershlag, she took her grandmother's maiden name, Portman, for her stage name.
(Columbia Pictures)
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Editor's note:
This image contains graphic content that some viewers may find disturbing.